[PATCH 1/7] rust: kunit: support KUnit-mapped `assert!` macros in `#[test]`s

Miguel Ojeda
2025-05-02T21:51:52Z

The KUnit `#[test]` support that landed recently is very basic and does
not map the `assert*!` macros into KUnit like the doctests do, so they
panic at the moment.

Thus implement the custom mapping in a similar way to doctests, reusing
the infrastructure there.

In Rust 1.88.0, the `file()` method in `Span` may be stable [1]. However,
it was changed recently (from `SourceFile`), so we need to do something
different in previous versions. Thus create a helper for it and use it
to get the path.

With this, a failing test suite like:

#[kunit_tests(my_test_suite)]
mod tests {
use super::*;

#[test]
fn my_first_test() {
assert_eq!(42, 43);
}

#[test]
fn my_second_test() {
assert!(42 >= 43);
}
}

will properly map back to KUnit, printing something like:

[ 1.924325] KTAP version 1
[ 1.924421] # Subtest: my_test_suite
[ 1.924506] # speed: normal
[ 1.924525] 1..2
[ 1.926385] # my_first_test: ASSERTION FAILED at rust/kernel/lib.rs:251
[ 1.926385] Expected 42 == 43 to be true, but is false
[ 1.928026] # my_first_test.speed: normal
[ 1.928075] not ok 1 my_first_test
[ 1.928723] # my_second_test: ASSERTION FAILED at rust/kernel/lib.rs:256
[ 1.928723] Expected 42 >= 43 to be true, but is false
[ 1.929834] # my_second_test.speed: normal
[ 1.929868] not ok 2 my_second_test
[ 1.930032] # my_test_suite: pass:0 fail:2 skip:0 total:2
[ 1.930153] # Totals: pass:0 fail:2 skip:0 total

Link: https://github.com/rust-lang/rust/pull/140514 [1]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
init/Kconfig | 3 +++
rust/Makefile | 3 ++-
rust/kernel/kunit.rs | 1 -
rust/macros/helpers.rs | 16 ++++++++++++++++
rust/macros/kunit.rs | 28 +++++++++++++++++++++++++++-
rust/macros/lib.rs | 4 ++++
6 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 63f5974b9fa6..5f442c64c47b 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -140,6 +140,9 @@ config LD_CAN_USE_KEEP_IN_OVERLAY
config RUSTC_HAS_COERCE_POINTEE
def_bool RUSTC_VERSION >= 108400

+config RUSTC_HAS_SPAN_FILE
+ def_bool RUSTC_VERSION >= 108800
+
config PAHOLE_VERSION
int
default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))
diff --git a/rust/Makefile b/rust/Makefile
index 3aca903a7d08..075b38a24997 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -402,7 +402,8 @@ quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
-Clink-args='$(call escsq,$(KBUILD_PROCMACROLDFLAGS))' \
--emit=dep-info=$(depfile) --emit=link=$@ --extern proc_macro \
--crate-type proc-macro \
- --crate-name $(patsubst lib%.$(libmacros_extension),%,$(notdir $@)) $<
+ --crate-name $(patsubst lib%.$(libmacros_extension),%,$(notdir $@)) \
+ @$(objtree)/include/generated/rustc_cfg $<

# Procedural macros can only be used with the `rustc` that compiled it.
$(obj)/$(libmacros_name): $(src)/macros/lib.rs FORCE
diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs
index 1604fb6a5b1b..2659895d4c5d 100644
--- a/rust/kernel/kunit.rs
+++ b/rust/kernel/kunit.rs
@@ -323,7 +323,6 @@ mod tests {

#[test]
fn rust_test_kunit_example_test() {
- #![expect(clippy::eq_op)]
assert_eq!(1 + 1, 2);
}

diff --git a/rust/macros/helpers.rs b/rust/macros/helpers.rs
index a3ee27e29a6f..57c3b0f0c194 100644
--- a/rust/macros/helpers.rs
+++ b/rust/macros/helpers.rs
@@ -86,3 +86,19 @@ pub(crate) fn function_name(input: TokenStream) -> Option<Ident> {
}
None
}
+
+pub(crate) fn file() -> String {
+ #[cfg(not(CONFIG_RUSTC_HAS_SPAN_FILE))]
+ {
+ proc_macro::Span::call_site()
+ .source_file()
+ .path()
+ .to_string_lossy()
+ .into_owned()
+ }
+
+ #[cfg(CONFIG_RUSTC_HAS_SPAN_FILE)]
+ {
+ proc_macro::Span::call_site().file()
+ }
+}
diff --git a/rust/macros/kunit.rs b/rust/macros/kunit.rs
index 4f553ecf40c0..eb4f2afdbe43 100644
--- a/rust/macros/kunit.rs
+++ b/rust/macros/kunit.rs
@@ -101,6 +101,8 @@ pub(crate) fn kunit_tests(attr: TokenStream, ts: TokenStream) -> TokenStream {
// ```
let mut kunit_macros = "".to_owned();
let mut test_cases = "".to_owned();
+ let mut assert_macros = "".to_owned();
+ let path = crate::helpers::file();
for test in &tests {
let kunit_wrapper_fn_name = format!("kunit_rust_wrapper_{}", test);
let kunit_wrapper = format!(
@@ -114,6 +116,27 @@ pub(crate) fn kunit_tests(attr: TokenStream, ts: TokenStream) -> TokenStream {
test, kunit_wrapper_fn_name
)
.unwrap();
+ writeln!(
+ assert_macros,
+ r#"
+/// Overrides the usual [`assert!`] macro with one that calls KUnit instead.
+#[allow(unused)]
+macro_rules! assert {{
+ ($cond:expr $(,)?) => {{{{
+ kernel::kunit_assert!("{test}", "{path}", 0, $cond);
+ }}}}
+}}
+
+/// Overrides the usual [`assert_eq!`] macro with one that calls KUnit instead.
+#[allow(unused)]
+macro_rules! assert_eq {{
+ ($left:expr, $right:expr $(,)?) => {{{{
+ kernel::kunit_assert_eq!("{test}", "{path}", 0, $left, $right);
+ }}}}
+}}
+ "#
+ )
+ .unwrap();
}

writeln!(kunit_macros).unwrap();
@@ -152,7 +175,10 @@ pub(crate) fn kunit_tests(attr: TokenStream, ts: TokenStream) -> TokenStream {
}
}

- let mut new_body = TokenStream::from_iter(new_body);
+ let body = new_body;
+ let mut new_body = TokenStream::new();
+ new_body.extend::<TokenStream>(assert_macros.parse().unwrap());
+ new_body.extend(body);
new_body.extend::<TokenStream>(kunit_macros.parse().unwrap());

tokens.push(TokenTree::Group(Group::new(Delimiter::Brace, new_body)));
diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs
index 9acaa68c974e..8bd7906276be 100644
--- a/rust/macros/lib.rs
+++ b/rust/macros/lib.rs
@@ -6,6 +6,10 @@
// and thus add a dependency on `include/config/RUSTC_VERSION_TEXT`, which is
// touched by Kconfig when the version string from the compiler changes.

+// TODO: check that when Rust 1.88.0 is released, this would be enough:
+// #![cfg_attr(not(CONFIG_RUSTC_HAS_SPAN_FILE), feature(proc_macro_span))]
+#![feature(proc_macro_span)]
+
#[macro_use]
mod quote;
mod concat_idents;
--
2.49.0